In normal conditions you can check for a ZWJ, but with regional coding chars, you would have to consider the regional chars block as a single char in the revers

In normal conditions you can check for a ZWJ, but with regional coding chars, you would have to consider the regional chars block as a single char in the reversal. Given that is isn't necessarily locale dependant but presentation layer dependant, there might not be anough info to decide how to act.